1. Field of the Invention
This invention relates generally to optical readers and more particularly, but not by way of limitation, to an optoelectronic system for automatically converting graphic data contained on a drill stem test chart into electrical binary signals.
2. Desciption of Related Art
During the drilling of an oil or gas well it is often desirable to determine the pressure-flow characteristics of the formation into which the well is drilled. This is desirable because the formation pressure-flow information can assist a properly trained person in evaluating whether the well is more or less likely to produce and, if it is likely to produce, in what relative quantities it can be expected to produce. A formation pressure response can also be used to determine what type of well treatment is advisable. Such a determination can be made because the transient response of the formation pressure as a function of time provides means for determining the permeability and other properties of the reservoir. In general, the information which can be derived from a formation pressure-flow reading can be used by the well operator to decide whether to complete, stimulate or abandon the formation.
One manner of obtaining formation pressure-flow data and of analyzing this data is to perform a drill stem test which includes placing a bourdon tube pressure recording device in a test string which is lowered into the well in which the formation pressure is to be recorded. Attached to the bourdon tube is a marking stylus which scribes, in response to formation pressures sensed by the bourdon tube, a graph on a black-coated metal drill stem test chart which moves relative to the stylus. The resultant graph is a record of the pressure sensed by the bourdon tube as a function of time.
Once such a drill stem test chart has been marked at the drill site with a pressure graph, the chart is mailed to a company which provides the service of analyzing the graphic data contained on the chart. Such a company has skilled employees who manually read the chart and convert the graphic data into numerical form for mathematical manipulation by a computer or other calculating means. The computer or other calculating means translates the actual test data (i.e., the converted graphic data) into formation properties needed to guide the well operator's decision to complete, stimulate or abandon the formation. The translation occurs through the use of basic equations and formulas generally known in the reservoir evaluation art.
As the translation process occurs, and thereafter, an expert analyzes the information and prepares a written report containing the facts and the opinions of the expert which the well operator uses in formulating his opinion. Once the report is completed, it is mailed to the customer or well owner.
This manner of processing formation pressure data is time-consuming because mailing the chart to an analysis company, waiting for the analysis to be made, and receiving the report of the analysis by return mail takes several days. The manual reading of each pressure chart also consumes time and permits human error to occur because of the difficulty in accurately and consistently reading charts of the type produced by the aforementioned manner of recording formation pressure. These shortcomings of this type of system are critical because during the interim between the preparation of the formation pressure chart and the receipt of the report, the drilling operation ceases. This is costly because the per day expenses for a drilling rig and a crew can be thousands of dollars.
Another system for preparing and analyzing formation pressure charts includes the utilization of one or more experts in the field at the drilling site. These experts read the charts prepared with a bourdon tube pressure recording device and manually convert the graphic data into numerical form for entry into a computer or other calculating means located either at the drilling site or remotely therefrom.
A shortcoming of this system is the expense of having one or more experts maintained in the field. Additionally, there are not enough qualified experts to be retained on each site of all wells when it is necessary to prepare and analyze formation pressure charts. Still further, the manual conversion of the chart indicia into numerical format consumes time and permits human error to occur.
Still another system for recording formation pressure and for analyzing the pressure data includes real-time electronic sensing and encoding means placed in a downhole tool. Such means senses the pressure and converts it into numerical format for transmission to a computer electrically connected to the sensing and encoding means.
Although such a system saves the time and expense of having an expert read and convert the chart from graphic format to numerical format, this third system is expensive because of the nature of the equipment necessary to construct the system. Additionally, to permit electrical communication between the downhole tool and the equipment located at the surface, a wireline must be run into the well. The presence of the wireline in the hole increases the hazard of blow-outs as known in the art. Still further, this third system is susceptible to malfunction in high temperature areas which are often encountered when making formation pressure recordings.
In view of the shortcomings of the aforementioned systems, there is the need for a system which can relatively quickly automatically convert graphic data (such as appears on a formation pressure chart) or other indicia into electrical signals for computerized numerical processing, which can relatively quickly transfer these signals from a field site at which the data are obtained to an analysis station for calculation and evaluation purposes so that delays through the mail are prevented, and which can prepare a report for transfer back to the field site.
To make such a system compatible with existing tools, such as a bourdon tube pressure recording device and the charts produced thereby, and to reduce the time and expense of having experts manually read the charts, the system should include means for automatically optically reading a chart (or other medium) having graphic or other data scribed or otherwise contained thereon.
It is to such an optical reading means that the present invention is directed. For the disclosure of an example of an overall system in which the present invention is contemplated to be used, reference can be made to the copending patent application of John E. Mosier, Jim B. Surjaatmadja, George B. McLawhon, and Jack C. Penn entitled DATA CONVERSION, COMMUNICATION AND ANALYSIS SYSTEM, U.S. patent application Ser. No. 355,317, filed Mar. 8, 1982, now U.S. Pat. No. 4,531,189.